be in cahoots

To be working together in secret, often with an air of unseemliness. Those two have been whispering all day. I wonder what they're in cahoots about. I think all of those kids are in cahoots because they're all on the surveillance video from the night of the robbery. It turned out that the business tycoon was in cahoots with local law enforcement to have the investigation dropped.

be in caˈhoots (with somebody)

(informal) be planning or doing something dishonest with somebody else: Some people believe that the company directors are in cahoots with the government.